A filter with dielectric resonator comprises at least one resonant cavity in which is installed a dielectric resonator and RF microwave energy coupling means making it possible to introduce RF energy at the input of the filter and to extract RF energy at the output of the filter. This type of filter can be excited only in a relatively narrow frequency band around the resonance frequency of the resonator which is generally adjusted by frequency tuning means.
However, the resonant cavities are subject to temperature variations, linked to the thermal environment and to the dissipated RF power, which provoke dimensional variations of thermoelastic origin and induce a shift in their resonance frequency. To remedy this major drawback, a first solution consists in using a dielectric resonator made of a dielectric material, of ceramic type, consisting of a mixture of a base material and one or more additional temperature compensation materials. Now, these additional materials introduce significant insertion losses which limit their use for the filtering of signals in high-power applications, such as, for example, in the output multiplexers of Omux type.
Another solution consists in using a dielectric resonator made of a dielectric material that is not temperature compensated, this material being able, for example, to consist of a base material of ceramic type such as, for example, alumina, the base material not having any additional compensation material. In this case, to enable the filter to overcome the temperature variations linked to both the thermal environment and the dissipated RF power, the filter can be fitted with a mechanical compensation device which makes it possible to dynamically control the resonance frequency of the cavity.
There are many mechanical compensation devices for a filter, such as, for example, in a first variant of the technological family, devices that use means for deforming an end wall called cap, or, in a second variant of the technological family, devices that use a translationally mobile part which passes through the wall of the filter and penetrates to a greater or lesser depth according to the temperature inside the cavity so as to control and stabilize the resonance frequency. However, since the compensation systems deriving from the first technological variant have to be mechanically coupled to the caps of the filter, they are suited to a filter topology with lateral input/output and cannot be applied to a filter with dielectric resonator in which the input and the output of the filter are axial. Moreover, in the second technological variant, since the mobile part has to slide in a hole situated on the body of the filter to be depressed in or withdrawn, the presence of a play that is necessary for the sliding requires implementing internal devices such as RF barriers or conductive flexible jackets, in order to provide the requisite RF performance levels in terms of or power behaviour losses, or even to overcome any electrical discontinuity effect.